Field of the Invention
The present invention relates to a semiconductor device and a power source supply method.
Description of the Related Art
Ordinarily, drive voltage for semiconductor devices is not communalized, and an appropriate driving voltage is specified for each semiconductor device. Accordingly, when, for example, a product that combines plural semiconductor devices is designed, each semiconductor device needs to be supplied with the drive voltage specified therefor.
For example, a method is known in which, when the drive voltage of a control semiconductor device that controls a driven semiconductor device that is one semiconductor device, is higher than the drive voltage of a driven semiconductor device that is another semiconductor device, a power source is connected to the control semiconductor device, a voltage of an input power source is lowered to the drive voltage of the driven semiconductor devices by a regulator installed in the control semiconductor device, and supplied to the driven semiconductor devices (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2003-143000 (Patent Document 1) and JP-A No. H11-45947 (Patent Document 2)).
However, it is assumed that, for example, a stabilized power source known as a switching power source is employed as the power source supplied to the semiconductor device in Patent Document 1 and Patent Document 2.
However, development of, for example, solar panels that use sunlight to generate electricity is advancing with the increased usage of renewable energy in recent years, and solar panels having high power generation efficiency can be obtained at a lower cost than hitherto. Although this makes it conceivable to employ solar panels as power sources supplied to semiconductor devices, time is needed for an output voltage of the solar panel to reach the drive voltage of the semiconductor device when employed in a dark situation in which the environment of the solar panel is below a specified brightness due to the weather, the time of day, or the like. Accordingly, until the output voltage of the solar panel reaches the drive voltage of the semiconductor device (during a drive transition time), the only current supplied to the semiconductor device is lower than a current corresponding to the drive voltage of the semiconductor device.
Accordingly, startup control from the control semiconductor device to the driven semiconductor device is unstable during the drive transition time due to overcharging when attempting to start up the driven semiconductor device from the control semiconductor device, which has a different drive voltage from the driven device.
In order to stably execute startup control from the control semiconductor device to the driven semiconductor device during the drive transition time, a circuit, for executing startup control of the driven semiconductor device even when the current is lower than the current corresponding to the drive voltage, needs to be added to the control semiconductor device. It is therefore anticipated that simply replacing the power source supplied to the semiconductor devices of Patent Document 1 and Patent Document 2 with a solar panel will make the operation of the semiconductor device unstable during the drive transition time.
Moreover, circuits that execute startup control of a driven semiconductor device during the drive transition time are generally complicated, and adding such a circuit to a control semiconductor device increases the cost of the control semiconductor device, and makes the size of the control semiconductor device even greater than before addition of the circuit.